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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | STANDARDS | HISTORY | BUGS | EXAMPLES | SEE ALSO | COLOPHON |
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LIST(3) Library Functions Manual LIST(3)
LIST_EMPTY, LIST_ENTRY, LIST_FIRST, LIST_FOREACH, LIST_HEAD,
LIST_HEAD_INITIALIZER, LIST_INIT, LIST_INSERT_AFTER,
LIST_INSERT_BEFORE, LIST_INSERT_HEAD, LIST_NEXT, LIST_REMOVE -
implementation of a doubly linked list
Standard C library (libc, -lc)
#include <sys/queue.h>
LIST_ENTRY(TYPE);
LIST_HEAD(HEADNAME, TYPE);
LIST_HEAD LIST_HEAD_INITIALIZER(LIST_HEAD head);
void LIST_INIT(LIST_HEAD *head);
int LIST_EMPTY(LIST_HEAD *head);
void LIST_INSERT_HEAD(LIST_HEAD *head,
struct TYPE *elm, LIST_ENTRY NAME);
void LIST_INSERT_BEFORE(struct TYPE *listelm,
struct TYPE *elm, LIST_ENTRY NAME);
void LIST_INSERT_AFTER(struct TYPE *listelm,
struct TYPE *elm, LIST_ENTRY NAME);
struct TYPE *LIST_FIRST(LIST_HEAD *head);
struct TYPE *LIST_NEXT(struct TYPE *elm, LIST_ENTRY NAME);
LIST_FOREACH(struct TYPE *var, LIST_HEAD *head, LIST_ENTRY NAME);
void LIST_REMOVE(struct TYPE *elm, LIST_ENTRY NAME);
These macros define and operate on doubly linked lists.
In the macro definitions, TYPE is the name of a user-defined
structure, that must contain a field of type LIST_ENTRY, named
NAME. The argument HEADNAME is the name of a user-defined
structure that must be declared using the macro LIST_HEAD().
Creation
A list is headed by a structure defined by the LIST_HEAD() macro.
This structure contains a single pointer to the first element on
the list. The elements are doubly linked so that an arbitrary
element can be removed without traversing the list. New elements
can be added to the list after an existing element, before an
existing element, or at the head of the list. A LIST_HEAD
structure is declared as follows:
LIST_HEAD(HEADNAME, TYPE) head;
where struct HEADNAME is the structure to be defined, and struct
TYPE is the type of the elements to be linked into the list. A
pointer to the head of the list can later be declared as:
struct HEADNAME *headp;
(The names head and headp are user selectable.)
LIST_ENTRY() declares a structure that connects the elements in
the list.
LIST_HEAD_INITIALIZER() evaluates to an initializer for the list
head.
LIST_INIT() initializes the list referenced by head.
LIST_EMPTY() evaluates to true if there are no elements in the
list.
Insertion
LIST_INSERT_HEAD() inserts the new element elm at the head of the
list.
LIST_INSERT_BEFORE() inserts the new element elm before the
element listelm.
LIST_INSERT_AFTER() inserts the new element elm after the element
listelm.
Traversal
LIST_FIRST() returns the first element in the list, or NULL if the
list is empty.
LIST_NEXT() returns the next element in the list, or NULL if this
is the last.
LIST_FOREACH() traverses the list referenced by head in the
forward direction, assigning each element in turn to var.
Removal
LIST_REMOVE() removes the element elm from the list.
LIST_EMPTY() returns nonzero if the list is empty, and zero if the
list contains at least one entry.
LIST_FIRST(), and LIST_NEXT() return a pointer to the first or
next TYPE structure, respectively.
LIST_HEAD_INITIALIZER() returns an initializer that can be
assigned to the list head.
BSD.
4.4BSD.
LIST_FOREACH() doesn't allow var to be removed or freed within the
loop, as it would interfere with the traversal.
LIST_FOREACH_SAFE(), which is present on the BSDs but is not
present in glibc, fixes this limitation by allowing var to safely
be removed from the list and freed from within the loop without
interfering with the traversal.
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/queue.h>
struct entry {
int data;
LIST_ENTRY(entry) entries; /* List */
};
LIST_HEAD(listhead, entry);
int
main(void)
{
struct entry *n1, *n2, *n3, *np;
struct listhead head; /* List head */
int i;
LIST_INIT(&head); /* Initialize the list */
n1 = malloc(sizeof(struct entry)); /* Insert at the head */
LIST_INSERT_HEAD(&head, n1, entries);
n2 = malloc(sizeof(struct entry)); /* Insert after */
LIST_INSERT_AFTER(n1, n2, entries);
n3 = malloc(sizeof(struct entry)); /* Insert before */
LIST_INSERT_BEFORE(n2, n3, entries);
i = 0; /* Forward traversal */
LIST_FOREACH(np, &head, entries)
np->data = i++;
LIST_REMOVE(n2, entries); /* Deletion */
free(n2);
/* Forward traversal */
LIST_FOREACH(np, &head, entries)
printf("%i\n", np->data);
/* List deletion */
n1 = LIST_FIRST(&head);
while (n1 != NULL) {
n2 = LIST_NEXT(n1, entries);
free(n1);
n1 = n2;
}
LIST_INIT(&head);
exit(EXIT_SUCCESS);
}
insque(3), queue(7)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.15 2025-05-17 LIST(3)
Pages that refer to this page: man-pages(7), queue(7)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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